1. Field of the Invention
This invention relates to a magnetic bubble information writing device, and more particularly, it relates to an information writing device capable of writing new information without erasing old one.
2. Description of the Prior Art
In has been known that electric current through a conductor loop disposed on a sheet of magnetic material can nucleate a bubble domain with a bias field substantially normal to the plane of the sheet, magnetic patterns of high permeability disposed on a surface of the sheet, and a rotating magnetic field which is parallel to the surface of the sheet. To nucleate the bubble domain, the electric current flows through the conductor loop, of course, in such a direction that a magnetic field produced by the electric current has an opposite direction to that of the bias field. To annihilate the bubble domain, the direction is reversed, i.e. an electric furrent flows through the conductor loop in such a direction that a magnetic field produced by the electric current strengthen the bias field. In a magnetic information storage device, the presence and absence of the bubble domain corresponds to a digital information, e.g. "1" and "0", respectively.
A conventional magnetic bubble information writing device consisting of the conductor loop was always preceded by an information erasing device just as a magnetic tape recorder. That is, the erasing device annihilates all the bubbles belonging to an old information and in the writing device an electric current flows always in a predetermined direction, and the presence and absence of the electric current corresponds to the digital information to be written. This writing system has an disadvantage that it is so complicated that external leads decrease the reliability of the information storage device and that operating margin is also decreased. Another fault is that the cycle time of the writing operation is relatively long.